Frist Draft (in this forum): Enum Parameters

[Paul Backus]

On Thursday, 25 April 2024 at 17:56:59 UTC, Quirin Schroll wrote:
> https://github.com/Bolpat/DIPs/blob/2bfef0b05e99c5448b416078da2e743482e3193d/DIPs/1NNN-QFS.md

Yet another non-orthogonal language feature that all generic code 
will have to go out of its way to account for until the end of 
time. `ref` is already bad enough; the last thing we need is 
another feature that repeats the exact same design mistakes.

For example: currently, in order to forward an argument correctly 
in generic code, we must write the following:

```d
void forwardTo(alias fun, T)(auto ref T arg)
{
     import core.lifetime: forward;
     fun(forward!arg);
}
```

Notice how much overhead is required *just* to deal with the 
`ref` storage class.

If this proposal were accepted, we would have to replace all 
instances of the above with the following:

```d
void forwardTo(alias fun, T)(auto enum auto ref T arg)
{
     import core.lifetime: forward;
     static if (__traits(isEnum, arg))
         fun(arg);
     else
         fun(fporward!arg);
}
```

Needless to say, the vast majority of D programmers are not going 
to bother with this, which means that we will forever be plagued 
by buggy handling of `enum` parameters in our library code (just 
as we are already plagued by buggy handling of `ref` parameters).

I do not think it is a good idea to introduce language features 
that set future D programmers up for failure like this.